This document relates to the concept of utilizing microwave radiation to activate a binder and enhance the desirable characteristics of the binder when used in the production of agglomerated products from particulate materials and binders. More specifically, agglomerating products made with microwave activated binders generally show a surprising improvement in compressive strength and in many cases also demonstrate an improved resistance to attrition (attrition index).
While agglomerating products made with the current method will have a number of ultimate uses and applications, the production of agglomerated fuel products is of particular interest. An estimated 2 billion tons of recoverable coal fines have been discarded in impoundments in the US with about 50 millions more tons added each year. This is a substantial resource that can be economically cleaned and separated into a low-ash product. However, it is not yet economically feasible to utilize such recovered fines due to obstacles associated with handling and high moisture content (i.e., low net Btu content). Drying and then forming the coal fines into agglomerates via briquetting, pelletization, extrusion, or other agglomeration techniques yields a product that is amenable to transport, storage, and handling in conventional coal-processing equipment Likewise, while there is a growing demand for ‘green energy’ that could be supplied to some extent by timber and agricultural waste residues, the low energy density of this material coupled with the costs for transport, processing, storage, and combustion of this material represents a formidable obstacle to utilization.
Extrusion is the most common technology for forming biomass into a pelletized fuel. However, extrusion is an energy intensive process that is limited in capacity, problematic to maintain a consistent production rate, and leads to excessive equipment erosion due to the high pressure required. The growing market for ‘green energy’ could be supplied more cheaply by direct briquetting of the biomass or the co-briquetting of biomass and coal fines. This may be particularly true for briquetting of biomass as briquetting is a lower-energy, higher-throughput, and lower-equipment erosion technology compared to extrusion. However, two of the more daunting economic obstacles to producing briquettes are the 1) cost of drying the fine coal and/or biomass and 2) binder costs. The present methods address both of these obstacles.